1. Field of the Invention
This invention pertains to high capacity batteries suitable for fast charging, and more specifically to a high capacity battery including an integrally-powered cooling assembly, for maintaining optimal efficiency in normal power supply operation, as well as in a fast charging mode.
2. Description of the Related Art
In the use of batteries as power supplies for vehicles, monitoring and surveillance installations, portable signage, temporary lighting units, and other applications, rechargeable high capacity batteries capable of being reenergized by fast charging have assumed increasing importance, due to their efficiency and their minimal down-time for recharging.
“High capacity batteries” as used herein refers to batteries of greater than about 100 Amp-hours capacity.
“Fast charging” as used herein refers to charging a battery at a rate of greater than 30 amperes per 100 ampere-hours of battery capacity. A goal of fast charging is to bring the state of charge (“SOC”) of a battery from 30% to 80% of full charge in less than about 1.5 hours.
U.S. Pat. No. 6,803,746 issued Oct. 12, 2004 in the names of the present inventors for “FAST CHARGER FOR HIGH CAPACITY BATTERIES,” describes high-efficiency fast chargers for fast charging of high-capacity batteries. The disclosure of such patent is hereby incorporated herein by reference, for all purposes.
As disclosed in the background section of such patent, conventional battery chargers typically operate at charging rates that are about or below 20 amperes per 100 ampere-hours of battery capacity. In consequence, the charging rate of such conventional battery chargers decreases early in the charge cycle, and 8-12 hours are required to restore the battery to full charge status.
The fast charger apparatus and method disclosed in U.S. Pat. No. 6,803,746 overcomes the deficiencies of conventional charging approaches, and permits high capacity lead-acid batteries to be safely charged at higher currents, in a highly effective manner, bringing batteries from 30% to 80% state of charge in about an hour. The charging enabled by the fast charging system of U.S. Pat. No. 6,803,746 is on the order of 400% faster than conventional charging technologies.
By such high-rate, high-efficiency charging afforded by the fast charging system described in U.S. Pat. No. 6,803,746, it is possible to operate fleets of battery-powered vehicles without changing out batteries, thereby obviating the time, effort and lost productivity costs of such change-outs. The fast charging system of U.S. Pat. No. 6,803,746 thereby permits a substantial increase in fleet productivity for such electric battery-powered vehicles. As a result, a typical operation requires at least 50% fewer batteries, in addition to the power savings realized by such systems.
In operation, high capacity batteries entail unique thermal management issues. During heavy duty operation of the power-consuming vehicle or installation, involving a substantial flow of electrochemically generated current, the high capacity battery “runs hot” and the temperature of the battery may rise as much as 20-30° F. or even more.
Additionally, the high-rate intensive charging enabled by the apparatus and method disclosed in U.S. Pat. No. 6,803,746, together with the accompanying continuous use of the high capacity battery that is enabled by such fast charging capability, e.g., with high capacity batteries used to power forklift vehicles in a heavy two or three shift operation without traditional “cool down” periods (which take place when batteries are changed out in prior conventional practice, and the out-changed batteries are put on conventional “slow charger” units overnight for recharging), produces substantial increases in battery temperature during the fast charging operation. This in turn requires charging current to be reduced during late-stage fast charging, in order to maintain battery temperature at a safe level to achieve desired battery life.
This occurrence of substantial increases in battery temperature during fast charging and heavy use applications has a number of adverse effects. Higher battery temperatures result in reduced battery life potentially causing warranty issues with the battery, as well as increasing operating expenses and cost-of-ownership (COO) of the battery-powered vehicle or installation. Further, where the battery (e.g., in a battery box or other mounted arrangement) is located in close proximity to an operator of a battery-powered vehicle or installation, the waste heat generated may adversely impact the operator, with consequent reduction of safety and desirability of the battery-powered operation. In addition, substantial increases in battery temperature undesirably impacts the fast charging operation by increasing the time required for a battery to achieve a targeted state of charge. As a result, the potential benefits inherent in fast charging are not fully realized.